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Biomedical subjects

B M Pratt

Publications and source records attributed to B M Pratt.

30 records · Page 2Linked to original sources
PubMed1986

Endothelial cell proliferation during angiogenesis. In vitro modulation by basement membrane components.

Modulation of the behavior of microvascular endothelial cells during angiogenesis has been observed to correlate with changes in the extracellular matrix. These reports prompted a comparison of the growth of microvascular endothelial cells on monolayers of various matrix components in vitro. Over a 5 day period, the proliferation of these cells was significantly greater on laminin than on either plasma fibronectin, the interstitial collagen types I and III, or on the basement membrane collagen type IV. Proliferation of the microvascular endothelial cells was compared with that of bovine aortic endothelial cells and bovine aortic smooth muscle cells on the same matrices. All three cell types grew significantly more rapidly on laminin than on fibronectin. The aortic endothelial cells differed from their microvascular counterparts in that the growth of these large vessel endothelial cells on the collagenous matrices (types I and III, or type IV) was not significantly different from that observed for laminin, but was greater than the relatively slow growth seen on plasma fibronectin. Further comparison of the growth of the microvascular endothelial cells on the two basement membrane components, laminin and type IV collagen, demonstrated that the growth of these cells on laminin can be modulated by the presence of type IV collagen. This was true either if the two matrices were combined as a mixed layer, or if the laminin was specifically bound to a layer of type IV collagen, more closely simulating the distribution of these molecules in a basement membrane. Examination by immunoperoxidase of in vivo model of neovascularization in the murine cornea revealed a temporally staggered appearance of basement membrane components. The appearance of laminin was found to occur throughout the newly formed vessels, as well as in individual cells at the migrating, proliferating tips. In contrast, the appearance of type IV collagen correlated with lumen formation and was not detected at the vessel tips. The results of this study suggest that the temporally ordered synthesis of specific matrix components plays a significant role in orchestrating the growth and differentiation of endothelial cells during the highly integrated set of responses known as angiogenesis.

Animals↗
PubMed1985

Differential dysmorphogenesis induced by microinjection of an alkylating agent into rat conceptuses cultured in vitro.

A technique of microinjection of small quantities of teratogens into extraembryonic compartments or specific organ primordium of rat conceptuses of pregnancy day 11 is described. Conceptuses microinjected with 50 nl tissue culture medium developed normally for 44-45 hr when cultured in homologous rat serum, indicating that the microinjection procedure itself did not produce any deleterious effects on growth and differentiation of embryos. Microinjection of an alkylating agent, phosphoramide mustard dissolved in tissue culture medium, into the exocoelom produced anomalous embryogenesis, consisting of retarded embryonic growth, anomalies of the neural tube, and general necrosis of various organ primordia. In contrast, the embryonic development remained relatively unaffected by microinjection of identical amounts of this alkylating agent into the amniotic cavity. However, neural-tube differentiation was markedly affected when phosphoramide mustard was injected into anterior neural-tube fluid, producing anencephalic or microcephalic embryos without significant effect on postcephalic organ differentiation. The morphogenesis of the anterior limb was unaffected by local injection of the agent into somitic tissues adjacent to the presumptive limb-bud region. Therefore, it appears that differential dysmorphogenesis could be induced by microinjection of an alkylating agent into different conceptus compartments. These results indicate that even during early embryogenesis various cell types are not equally susceptible to a given teratogen, and that the differential cytotoxicity of the teratogen toward specific embryonic or extraembryonic cells and tissues may account for embryonic anomalies characteristically produced by that agent.

Abnormalities, Drug-Induced↗
PubMed1985

Immunolocalization of type IV collagen and laminin in nonbasement membrane structures of murine corneal stroma. A light and electron microscopic study.

The extracellular matrix of adult vertebrate corneal stroma is composed primarily of the interstitial collagen type I and smaller amounts of types III and V collagen. These collagens are organized into overlapping lamellae of striated filaments. In addition to these lamellar structures, the corneal stroma also contains 100- to 250-nm bundles of nonstriated 8- to 11-nm microfibrils. By immunofluorescent localization and electron microscopic immunolocalization, these microfibril bundles in the mouse are associated with type III collagen, type IV collagen, and laminin. By immunologic and histochemical criteria, these bundles do not contain either type I collagen, type V collagen, elastin, or oxytalan microfibrils. The cellular source, composition, and possible functions of these microfibril bundles are discussed.

Animals↗
PubMed1984

The ultrastructural organization and architecture of basement membranes.

Basement membranes are ubiquitous complex, multicomponent structures having diverse functions. They are morphologically distinct and exhibit specific structural details including the lamina rara and lamina densa. In addition, the interstitial stroma abutting the lamina densa has a unique organization. While the composition of basement membranes is still incompletely known, several components have been identified, including collagen types IV and V, laminin and heparan sulphate proteoglycan. High resolution immunoelectron microscopic studies have allowed the development of various models of the organization and architecture of the basement membrane, suggesting specific localizations of the various collagen types and specific domains of the collagen molecules, laminin and other components. In addition, high resolution metal shadow casting techniques have allowed the development of molecular models of specific components of the basement membrane and methods of studying the domain structure and interactions of these components.

Animals↗
PubMed1984

Mechanisms of cytoskeletal regulation. Modulation of aortic endothelial cell spectrin by the extracellular matrix.

Endothelial cells have a complex cytoskeleton that is responsive to a variety of stimuli such as shear and desquamative injury. The extracellular matrix is known to influence several aspects of cellular behavior, including attachment, spreading, and migration and may, in part, initiate and control vascular responses in growth, differentiation, wound repair, and neoplasia. It is likely that linkage between surface receptors responsible for sensing the matrix and the cytoskeleton may be relevant to understanding the mechanisms of these responses. Spectrin is a high-molecular-weight heterodimer recently identified in many cells that appears to link surface receptors to cortical actin filaments. We have confirmed the existence of spectrin in cultured aortic endothelial cells by metabolic labeling and immunoprecipitation and demonstrated that its organization and intracellular distribution is sensitive to the extracellular matrix. When bovine calf aortic endothelial cells (BAEC) are cultured to confluency on a fibronectin (Fn) substrate, they assume a flattened, spread morphology and exhibit a punctate spectrin distribution with no discernible peripheral localization. In contrast, BAECs cultured on a Type I/III collagen (I/III) substrate exhibit a fibrillar spectrin pattern with significant peripheral localization. When migrating cells were examined, the distribution of spectrin was strikingly different. The cells on the Fn substrate showed no changes in spectrin localization, whereas the cells on I/III exhibited a significant rearrangement, with spectrin being in a coarse fibrillar form, with the fibrils aligned parallel to the direction of migration. The differences in arrangement of this cytoskeletal component on the two substrata reflect the ability of the substrate to perturb the cytoskeletal organization and modulate some aspects of cell behavior such as spreading, proliferation, and migration. These data are consistent with the concept that the nonerythroid spectrins may function as transducers of information from membrane receptors to the cytoskeleton.

Animals↗
PubMed1983

The in vivo and in vitro effects of clomiphene citrate on ovulation, fertilization, and development of cultured mouse oocytes.

Clinical data indicate a high rate of discrepancy between ovulation and pregnancy rates and a high abortion rate in anovulatory women treated with clomiphene citrate. An animal model was used to examine the in vivo and in vitro effects of the drug on fertilization and preimplantation development. This work indicates that mice treated with clomiphene in the early follicular phase of pregnant mare's serum-induced cycles show a dose-dependent decrease in ovulated oocytes. No effect was seen on the further development of these ova. When the drug was administered in the late follicular phase, a dose-dependent decrease was seen in the rate of successful copulation, ovulation, and embryo development. Concomitant 17 beta-estradiol treatment reversed the copulatory, ovulatory, and developmental effects of clomiphene. A short in vitro treatment of oocytes with clomiphene prior to in vitro fertilization resulted in an increased proportion of degenerated and unfertilized ova. Moreover, this treatment caused a dose-dependent decrease in blastocyst formation.

Animals↗
PubMed1983

Effects of microphthalmic white (Miwh) on the number and function of cutaneous melanocytes.

Microphthalmic white (Miwh), when heterozygous, causes dilution of black fur to a uniform gray color. Miwh/+ also reduces the coloration of ear and tail skin. The present study, a quantitative assessment of the effects of Miwh/+ on cutaneous melanocytes, demonstrates that the primary effect of Miwh/+ on cutaneous pigmentation is to reduce the number of epidermal melanocytes. There is also indirect evidence that Miwh/+ reduces the rate of melanosome production within follicular melanocytes. These actions of Miwh/+ cause both lightened coloration of ear and tail skin and the deposition of fewer numbers of smaller melanosomes within the hair.

Animals↗
PubMed1982

Site of gene action of the white allele (Miwh) of the microphthalmia locus: a dermal-epidermal recombination study.

The white allele Miwh of the microphthalmia locus, when homozygous, causes a complete absence of neural crest-derived melanocytes in skin and internal organs. The site(s) of gene action of Miwh on melanoblast differentiation were examined by making dermal-epidermal recombinant grafts with skin from 13-14-day embryos of the following genotypes: normal (+/+), heterozygous white (Miwh/+), homozygous white (Miwh/Miwh), and dominant spotting (W/W). Based on results from these grafts, the following conclusions were reached: Miwh/Miwh epidermis is as effective as W/W epidermis in supporting the differentiation of +/+ follicular melanocytes. Miwh/Miwh dermis is completely permissive to in situ differentiation of +/+ follicular melanocytes. Thirteen-fourteen-day embryonic Miwh/Miwh skin, both epidermis and dermis, alters of blocks the differentiation of +/+ melanoblasts into dermal melanocytes. By 13 days of development, melanoblasts from both Miwh/+ and Miwh/Miwh skin, even when presented with a permissive W/W environment, are irreversibly redirected into abnormal developmental pathways resulting in either a reduction in follicular pigmentation (Miwh/+) or a complete absence of follicular melanocytes (Miwh/Miwh).

Alleles↗
PubMed1982

A study of ultrasound-induced microstreaming in blood vessels of tropical fish.

Tails of the tropical fish Xiphophorous maculatus have been studied by light microscopy during irradiation with continuous wave 780 kHz ultrasound. Acoustically-induced microstreaming was observed in blood vessels during irradiation with peak intensities above 1 Wcm-2. The microstreaming took the form of rotation of single blood cells and clusters of a few cells and occurred at positions close to the edges of cartilage rods supporting the tail. Streaming was detected initially in vessels 5-10 micrometers across where it impeded blood flow, and as the blood velocity fell it was also observed in larger vessels 15-30 micrometers across. Measurements of rotation speed showed that streaming velocity increased with intensity. The microstreaming is thought to result from radiation torque created by the complex standing wave field produced by reflection from the irradiation tank window and the cartilage rods, or by vibration of the rods in the sound field.

Animals↗
PubMedDate not supplied

Observations of ultrasound-induced effects in the fish Xiphophorous maculatus.

Tails of the fish Xiphophorous maculatus have been studied by transmission light microscopy during irradiation with continuous wave ultrasound (frequencies 0.78-3 MHz, spatial average intensities 0.01-3 Wcm-2). Blood flow started to increase a few minutes after the start of an irradiation, reaching a maximum after 5-10 min. Periodic variations in blood flow rate were often seen, and the response varied considerably among individual specimens. Acoustic microstreaming, which resulted in rapid rotation of clusters of cells, was observed in blood vessels adjacent to cartilaginous rods in the tail. The threshold average spatial intensities to initiate this were a few hundred mW cm-2 at 0.78, 1.5 and 3 MHz. The microstreaming resembled that occurring around ultrasonically stimulated microbubbles, but no evidence of any association was found. Microbubbles, possibly originating in water, were sometimes seen in the tissue of the fish following treatment with ultrasound.

Animals↗
PubMedDate not supplied

Blonde, a new mutation in Peromyscus maniculatus affecting fur, skin, and eye pigmentation.

An autosomal recessive mutation affecting hair and eye pigmentation was discovered in the F2 progeny of wild-type deer mice, (Peromyscus maniculatus), trapped near East Lansing, Michigan. When homozygous, the mutation (designated as blonde, bl), reduces both black and yellow pigmentation deposited in the fur, reduces or eliminates pigmentation in the non-follicular melanocytes of the outer ear, peri-orbital skin and tail, slightly reduces the amount of pigmentation in the choroidal melanocytes, and completely eliminates pigmentation of the retinal epithelium.

Animals↗